Physical and behavioral development of rodents were studied in the following ways: (a) 15 pairs of mice, each of which had siblings of comparable history remaining in a complex environment, were removed from this environment shortly after they attained reproductive capacity. Parental care-giving behavior of each of these pairs was studied in a small environment designed for this purpose. (b) Strains of wild Norway rats were screened for resistance to an anti-coagulant drug (Warfarin) to enlarge our stock of Norway rats suitable for pursuing developmental and other behavioral research. (c) Nest-building behavior of mice was recorded with respect to age, and social history. (d) As a part of a broader effort to develop a "catastrophe theory" formulation of behavioral states, motivation, drive, emotion, and mood. Focus was placed on two types of inter-response times characterizing lever pressing for water. (e) Circadian rhythms of mice by social history type and by type of behavior are being studied. This project includes parts of discontinued projects ZO1 MH 0025, 26, and 27. BIBLIOGRAPHIC REFERENCES: Calhoun, J.B.: Social modification of activity rhythm in rodents. In Proceedings, Twelfth International Conference - International Society for Chronobiology, Washington, August 10 - 13, 1975. Pp. 83-93. Publishing House I1 Ponte, Milano, Italy. 1977. 765 pp. In press. Stewart, J.M., Scott, J.P., and DeGhett, V.J.: The Development of Social Affects: Effects of early experience on separation distress. Revista Latino-Americana-de Psycologia. 9:(2): 247-257, 1977.